This invention relates generally to the field of intraocular lenses (IOL) and, more particularly, to anterior chamber phakic IOLs.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.
The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In the normal, healthy eye, sharp images are formed on the retina (emmetropia). In many eyes, images are either formed in front of the retina because the eye is abnormally long (axial myopia), or formed in back of the retina because the eye is abnormally short (axial hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. In addition, due to age-related reduction in lens accommodation, the eye may become presbyopic resulting in the need for a bifocal or multifocal correction device.
In the past, axial myopia, axial hyperopia and corneal astigmatism generally have been corrected by spectacles or contact lenses, but there are several refractive surgical procedures that have been investigated and used since 1949. Barraquer investigated a procedure called keratomileusis that reshaped the cornea using a microkeratome and a cryolathe. This procedure was never widely accepted by surgeons. Another procedure that has gained widespread acceptance is radial and/or transverse incisional keratotomy (RK or AK, respectively). Recently, the use of photablative lasers to reshape the surface of the cornea (photorefractive keratectomy or PRK) or for mid-stromal photoablation (Laser-Assisted In Situ Keratomileusis or LASIK) have been approved by regulatory authorities in the U.S. and other countries. All of these refractive surgical procedures cause an irreversible modification to the shape of the cornea in order to effect refractive changes, and if the correct refraction is not achieved by the first procedure, a second procedure or enhancement must be performed. Additionally, the long-term stability of the correction is variable because of the variability of the biological wound healing response between patients.
Permanent intracorneal implants made from synthetic materials are also known for the correction of corneal refractive errors. For example, U.S. Pat. No. 5,123,921 (Werblin, et al.) discloses an intracorneal lens that is implanted intrastromally using a microkeratome. The lens itself has little refractive power, but changes the refractive power of the cornea by modifying the shape of the anterior surface of the cornea. The microkeratome used to implant this lens is complex and expensive and the lens requires a great deal of surgical skill to implant.
Keravision owns a series of patents related to an intrastromal ring device used to induce refractive changes in the cornea (see U.S. Pat. Nos. 5,505,722, 5,466,260, 5,405,384, 5,323,788, 5,318,047, 5312,424, 5,300,118, 5,188,125, 4,766,895, 4,671,276 and 4,452,235). The use of a ring-shaped device avoids implantation of the device within the central optical zone of the cornea, and is implanted in peripheral groove made by a special surgical instrument. The ring itself has no refractive power. Refractive changes are caused by the implanted ring changing the shape of the anterior surface of the cornea.
A variation of the intrastromal ring is called Gel Injection Adjustable Keratoplasty (GIAK) and is described in U.S. Pat. Nos. 5,090,955 (Simon), 5,372,580 (Simon, et al.) and WIPO Publication No. WO 96/06584. Instead of a solid device, these publications disclose injecting a ring of biocompatible gel around the optic zone of the stroma to effect refractive changes to the cornea by changing the shape of the cornea.
These prior art intracorneal devices all work by changing the shape of the cornea, and the devices themselves have little or no refractive properties. As a result, the preparation of the lamellar bed into which these devices are inserted is critical to the predictability of the refractive outcome, requiring very precise microkeratomes or other special surgical instruments and a great deal of surgical skill for success.
Various intracorneal implants having a refractive power are also known. For example, U.S. Pat. No. 4,607,617 (Choyce) describes an implant made of polysulfone (refractive index 1.633). The high refractive index of polysulfone relative to stromal tissue (1.375) results in an implant that acts as an optical lens that effects a refractive change to the cornea without relying on a change in corneal shape. This lens was never clinically or commercially acceptable because the polysulfone material is too impermeable to glucose and other metabolites to maintain the corneal tissue anterior to the implant. Corneal ulcerations, opacifications and other complications were the clinical result.
An implant that attempts to overcome the complications of polysulfone implants is described in U.S. Pat. No. 4,624,669 (Grendahl). This implant contains a plurality of microfenestrations that allows the flow of glucose and other metabolites through the lens. In animal studies, however, the microfenestrations were filled with keratocytes that created opacities, resulting in unacceptable light scattering and visual acuities. As a result, this implant was never commercially developed. In an attempt to limit damage to the anterior cornea and prevent keratocyte ingrowth, U.S. Pat. No. 5,628,794 (Lindstrom) discloses a limited diameter (2.5 mm) refractive multifocal implant for correction of presbyopia made from a rigid material having fenestrations, the implant and the fenestrations being coated with a hydrogel material. The inventors are not aware of clinical data for this lens. This limited diameter multifocal lens is not clinically acceptable for monofocal correction of myopia or hyperopia in most patients with normal pupil size under normal environmental light conditions.
Previous attempts to correct presbyopic vision have generally been limited to spectacles or contact lenses. Recently, clinical investigations were initiated for a limited diameter (less than 2.5 mm), low water content (approximately 45%) monofocal hydrogel inlay that effectively created a multifocal cornea. These early clinical investigations; however, have not been encouraging due to compromised distance vision and unacceptable multifocal vision. These lens are described in U.S. Pat. Nos. 5,196,026 and 5,336,261 (Barrett, et al.).
Several companies are investigating implantable anterior chamber phakic IOLs, including Bausch & Lomb's NuVita and Model ZB5M lenses, and the Artisian iris claw lens by Ophtec BV. These and other anterior chamber phakic lenses are described in U.S. Pat. Nos. 5,071,432 (Baikoff), 5,192,319 (Worst), 5,300,117 (Baikoff, et al.), 5,928,282 (Nigam) and PCT Publication No. WO 98/56315. The clinic experience with commercially available anterior chamber phakic lenses has not been entirely satisfactory due to difficult implantation techniques and clinical complications such as endothelial cell loss and pupil ovaling.
Therefore, a need continues to exist for a safe and biocompatible anterior chamber phakic intraocular lens.